Centralized bicarbonate mixing system

ABSTRACT

A centralized bicarbonate mixing system is provided for a plurality of dialysis machines of a dialysis clinic. The system includes a source of purified water, a mix tank, an eductor having a hopper for receiving dry bicarbonate material, a mixing pump and a mixing conduit loop connecting the mixing pump, the eductor and the mix tank so that as water is circulated by the mixing pump through the mixing conduit loop, the dry bicarbonate material is drawn into the eductor and mixed with the water. The system further includes a circulation tank, and a transfer conduit connecting the mixing conduit loop to the circulation tank, so that a mixed bicarbonate solution can be transferred from the mixing conduit loop to the circulation tank. The system further includes a circulation pump, and a circulation supply conduit connecting the circulation tank and the circulation pump so that mixed bicarbonate solution can be pumped from the circulation tank to the dialysis machines. The system is preferably constructed of cross-linked polyethylene and/or polypropylene plastic pipe and fittings, and is provided with heat exchangers so that the same can be heat disinfected. Furthermore, the use of the eductor and closed hopper allows for easy loading of dry bicarbonate material into the system, and for sanitary mixing of a batch of bicarbonate solution in the closed system.

“This application is a division of our pending U.S. patent applicationSer. No. 09/586,094 filed Jun. 2, 2000, which parent application claimedbenefit of our provisional U.S. patent application Ser. No. 60/137,647filed Jun. 4, 1999.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to apparatus for mixingadditives and water for medical purposes, and more particularly, but notby way of limitation, to apparatus for mixing a bicarbonate solution foruse with dialysis machines.

2. Description of the Prior Art

Conventional prior art centralized mixing systems have used a mixingtank into which water was directed and into which bulk quantities ofpowered additives have been dumped into the open top of the tank. Thewater and dry additives are then mixed through the use of a mechanicalmixer. The mixed solution is then pumped to a storage tank from which itis delivered to the individual dialysis machines.

There are several problems with such systems. First, the mixing tank istypically an open top tank which allows the mixture to be contaminatedwhich leads to medical complications for the patients using the mixture.Second, it is physically difficult to lift the large bags of bulkmaterial into the open top tank, and the operation of this equipmentleads to many on-the-job injuries, such as back strains and the like.

Centralized bicarbonate systems are frequently cited as the source ofwater born bacteria and endotoxin. This probably results from theenhancement in the growing medium (permeate solution typically has toolittle nutrient to support bacteria growth) and the fact that the systemis open for charging and mixing for extended periods of time.

One other system which has been more recently developed to providepreparation of fluid concentrates is that shown in U.S. Pat. No.5,344,231 to Jonsson, et al. The Jonsson, et al. system utilizes acartridge apparatus for the mixing of concentrate and water at theimmediate location of the dialysis machine. The primary difficulty withthe Jonsson, et al. system is its high cost.

Thus, it is seen that there is a need in the art for improved systemsfor mixing of water and additives for medical uses, and particularly toprovide bicarbonate solution to dialysis machines, while eliminating theproblems of the various prior art systems discussed above.

SUMMARY OF THE INVENTION

The present invention provides a system for mixing water and an additiveto form a concentrate solution. The system includes a mix tank having anoutlet. A pump has a suction inlet connected to the outlet of the mixtank, and has a pump discharge. An eductor has a fluid inlet and a fluidoutlet with a flow path connecting the fluid inlet and the fluid outlet.The eductor has an eductor inlet connected to the flow path. The fluidinlet of the eductor is connected to the pump discharge. An additivecontainer has an outlet connected to the eductor inlet, so that additivestored in the additive container is drawn therefrom by the flow of fluidthrough the flow path of the eductor. A return line connects the fluidoutlet of the eductor to the mix tank. Thus, a closed system is providedin which water and the dry additives may be mixed by a combination ofthe mixing activity which takes place in the eductor and the pipingdownstream of the eductor and by further mixing action which takes placeas the mixture is re-circulated back through the mix tank.

The present invention is developed to reduce the opportunity for havingan open tank while preparing dialysate and to make the mixing processmore ergonomic and faster. This is accomplished by reducing the heightof the port for charging the solid bicarbonate powder, using a funneland ejector to wet and mix the powder with circulating permeate andagitating the mix tank with nozzles driven by the re-circulating flow offluid.

It is therefore a general object of the present invention to provide animproved system for mixing water and additives to form concentratesolutions for medical uses.

Still another object of the present invention is the provision of anadditive mixing system which is completely closed so as to preventcontamination of the solution.

Yet another object of the present invention is to provide a system formixing water and additives which does not require bags of additivepowder to be lifted overhead into large mixing tanks.

Still another object of the present invention is the provision ofsystems for mixing water and additives which are economical.

Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art uponreading of the following disclosure when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of the mixing system of the presentinvention.

FIG. 2 is a schematic illustration of the mixing system of FIG. 1.

FIG. 3 is a schematic illustration of a circulation tank and fluidsupply piping which is utilized with the mixing system of FIG. 2.

FIG. 4 is an enlarged sectioned schematic view of the eductor of thesystem of FIGS. 1 and 2.

FIG. 5 is a schematic illustration of a modified embodiment of theinvention showing the mixing system, along with the circulation systemand the dialysis clinic.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now the drawings, and particularly to FIG. 1, the system ofthe present invention is shown and generally designated by the numeral10. The system 10 may be described as a system for mixing water and anadditive to form a concentrate solution, and more particularly, as asystem for mixing a permeate solution with a dry additive powder such assodium bicarbonate to provide a sodium bicarbonate solution to beutilized by dialysis machines in a dialysis clinic.

The system 10 as shown in FIG. 1 includes a mix tank 12. The mix tank 12has a closed top 14 and a conical bottom 16 leading to a mix tank outlet18.

An outlet line 20 is connected to the outlet 18 and to a suction inlet22 of a pump 24. A valve 26 is located in the outlet line 20.

The pump 24 is a conventional centrifugal pump which takes fluid in thesuction inlet 22 and discharges the fluid at a pump discharge 28.

The pump discharge outlet 28 is connected to a discharge line 30 whichleads to an eductor 32. The eductor 32 may for example be a “Jet Pump”as available from the Penberthy Company of Prophetstown, Ill.

A schematic cross-sectional view of the eductor 32 is shown in FIG. 4.The eductor 32 includes a fluid inlet 34 which is connected by a flowpath 36 to a fluid outlet 38. An eductor inlet 40 is laterally connectedto the flow path 36 so that fluid flowing through the flow path 36 fromthe inlet 34 to the outlet 38 draws a suction on the eductor inlet 40which will, in turn, draw material into the eductor 32.

An additive container or hopper 42 is mounted on top of the eductor 32.The additive container has a top 44 which may be closed by a rotatablehatch 46. The additive container includes a conical shaped bottomportion 48 leading to a container outlet 50 which is connected to theeductor inlet 40 so that additive material stored in the additivecontainer 42 is drawn therefrom by the flow of fluid through the flowpath 36 of the eductor 32.

Upstream of the eductor inlet 34 there is a tee 62 contained in thedischarge line 30. The tee 62 is connected to a wash-down line 64 whichleads to a clean in place nozzle 66 located within the additivecontainer 42 for washing down the same. A valve 68 in the wash-down line64 controls the flow of fluid to the clean in place nozzle 66.

A return line 52 is connected to the outlet 38 of eductor 32 and returnsto the mixtank 12.

The return line 52 leads to a pair of offset laterally directed ejectionnozzles 54 and 56 disposed in the mix tank 12, so that fluid returned tothe mix tank 12 creates a swirling action in the mix tank to further mixthe water and additive within the mix tank 12.

The return line 52 also leads via valve 86 to a clean in place nozzle 88located within the mix tank 12 for aiding in cleaning the same.

It will be appreciated that the system 10 is a closed system. As will befurther described below with regard to FIG. 2, permeate or water isprovided to the tank 12 from a source and then is circulated through thesystem 10 in which the additive, which is placed in additive tank 42, ismixed with the permeate to provide the desired concentrate solution. Asfurther described below with regard to FIG. 2, the concentrate solutioncan then be directed to a storage and circulation tank from which itwill be provided to the individual dialysis machines.

Turning now to FIG. 2, the system 10 of FIG. 1 is there schematicallyillustrated and other details of the system are schematicallyillustrated.

The water or permeate solution which is to be mixed with the additive isprovided from a source 58 via supply line 60.

In the discharge line 30 there is a takeoff line 70 which is connectedto a circulation tank 72 of FIG. 3. The circulation tank 72 serves as acentral storage tank from which the bicarbonate solution may be suppliedto a series of dialysis machines in a dialysis clinic. The bicarbonatesolution 74 contained in the circulation tank 72 is pumped by a pump 76to a bicarbonate supply line 78 which leads to the dialysis machines andflows in a loop returning as bicarbonate return line 80 to thecirculation tank 72.

In general, the system of FIGS. 1 and 2 is operated in the followingmanner.

Permeate or water is provided from source 58 via supply line 60 to thesealed mix tank 12. The fluid is pumped from the mix tank 12 via pump 24through the eductor 32 and then back through the return line 52, thusproviding a closed circulating fluid flow loop. The desired quantity ofdry additive material is placed in the additive container 42 and is fedtherefrom into the eductor 32. The additive mixes with the fluid in theeductor 32 and the discharge line 52 and further mixes as it circulatesthrough the mix tank 12 where it is swirled due to the action of theejector nozzles 54 and 56.

The desired volume of water and additives such as sodium bicarbonate aremixed in the circulating system 10 until they are satisfactorily mixed.

For example, one suitable formula for mixing a batch of bicarbonatesolution is as follows. To make 50 gallons of solution, utilize 189.25liters of permeate, 12.48 kilograms of NAHCO3 premix power, and 4.46kilograms of NACL.

When a batch is satisfactorily mixed, it may be directed to thecirculation tank 74 by closing a valve 82 and opening a valve 84. Assoon as the batch of bicarbonate solution has been pumped into the tank72, the valve 82 is reopened and the valve 84 is closed.

Then the system 10 will be cleaned by washing the same with clean fluid,and the process can be repeated to make a new batch of bicarbonatesolution in the system 10 and then once again direct it to thecirculation tank 72.

It will be understood that the circulation tank 72 serves as a place forstorage of the mixed bicarbonate solution, and subsequent supply of thesame as needed to the individual dialysis machines.

DETAILED DESCRIPTION OF OPERATION AND HEAT DISINFECTION OF MIX TANKSYSTEM OF FIG. 2

To fill the mix tank 12 the following steps are conducted:

1. The mounting position for the capacitance switch cut off is selectedfor the desired volume of solution in the tank;

2. The valve designated HV2 is closed;

3. The valve HV1 is opened;

4. The “on” switch is depressed thus opening the normally closedsolenoid valve designated SV1;

5. The tank 12 is allowed to fill.

The operation of mixing the dry bicarbonate powder from hopper 42includes generally the following steps:

1. The desired amount of pre-mixed NAHCO3 is added to hopper 42 asrequired by the volume of solution to be mixed and the formula to beused;

2. The top of the hopper 42 is closed with lid 46;

3. Valve HV2 is opened and the circulation pump 24 is turned on. Notethat the discharge line 52 must be connected to the tank 12 through thevalve ported quick disconnect designated as VPQD4;

4. The permeate solution is circulated through the mixing loop until allof the dry powder material from hopper 42 is completely dissolved;

5. After complete dissolution, the powder mixer 32, 42 can be removedfrom the circulation loop on the fly with the pump 24 running byconnecting VPQD2 to VPQD3;

6. The mix tank 12 can remain circulating until it is desired totransfer its contents to the bicarbonate circulation tank 72;

7. The powder mixer 32, 42 should be flushed with permeate and allowedto drain and dry.

The sequence of operations for transferring bicarbonate solution fromthe mix tank 12 to the circulation tank 74 can be generally described asfollows:

1. Disconnect VPQD4 and make connection to VPQD6 on the circulation tank72;

2. Empty the mix tank 12 into the circulation tank 72;

3. Disconnect VPQD6 and reconnect to VPQD4;

4. Turn pump 24 off.

The sequence of operations for cleaning in place the system of FIG. 2and heat disinfecting the same generally includes the following:

1. Turn the capacitance level switch to the low level clean in placesetting;

2. Depress the fill switch, opening the permeate feed solenoid SV1;

3. Connect VPQD2 to heat exchanger HX-1 inlet;

4. Connect VPQD3 to heat exchanger HX-1 outlet;

5. Turn circulation pump 24 on;

6. After 30 minutes, break connection at VPQD4 and make connection atVPQD5 to flow fluid to clean in place nozzle 88;

7. Circulate water for at least 15 minutes and preferably about one-halfhour, maintaining temperature above 190° F.;

8. Break connection at VPQD5 and reconnect at drain air gap; and

9. Run contents to drain.

The normal operation of the circulating tank 72 in FIG. 3 is tocontinuously circulate via pump 76 through the bicarbonate supply line78 to the loop piping system directed to the dialysis clinic, whichreturns through bicarbonate return line 80.

When it is desired to heat clean in place the system of FIG. 3, thesequence of operations is generally as follows:

1. The remaining solution is drained from tank 72 and from the looppiping by breaking connection VPQD-10 and reconnecting to the air gapdrain;

2. After solution has been drained, the loop piping and tank 72 arefilled with permeate, circulating the permeate with pump 76. Afterfilling the tank with approximately 100 gallons of permeate, thepermeate fill valve HV-4 is closed;

3. The connection at VPQD8 is broken and the circulation is routedthrough heat exchanger HX-1;

4. The heated permeate is circulated until the temperature reaches 190°F. and is continued for 30 minutes;

5. The connection at VPQD10 is broken and then the connection at VPQD11is made, thus circulating the hot permeate through clean in place nozzledesignated as CIPN2;

6. The permeate is circulated in the manner described for 30 minutes,maintaining the temperature above 190° F.;

7. The connection at DPQD11 is broken and connected to VPQD13;

8. The contents are run to the drain. The draining of the system in thismanner will result in siphoning of the residual permeate from the pump76 and associated piping. No dialysis machines or other devices whichcould either receive hot permeate or give up contaminated fluids can beconnected to the bicarbonate loops while the clean in place operationsare being performed. VPQD13 is connected to a bimetallic temperaturesolenoid valve with a closing set point of 85° F. This functions topurge the hot disinfection fluid from the system, without loss of coolerpermeate that may be used as a flushing agent. VPQD12 is provided as anopen drain connection without proof of temperature for discharge; and

9. VPQD10 is reconnected and the circulation tank 72 is filled from themix tank 12 through VPQD6 as previously described.

THE EMBODIMENT OF FIG. 5

Turning now to FIG. 5, a modified embodiment is shown of the mixingsystem of the present invention is shown and generally designated by thenumeral 100. Many of the components of the system 100 are substantiallyidentical to those of the system 10 previously described, and likenumerals are used to identify the same.

The system 100 can be summarized as follows. The system includes asource 58 of purified water, the mix tank 12, the eductor 32 havinghopper 42, and a mixing pump 24. The system further includes a mixingloop 102 which connects the mix pump 24, the eductor 32 and the mix tank12. The mixing loop 102 includes the discharge line 30, the return line52, the outlet line 20, and the various items of equipment locatedtherein.

The system 10 further includes a transfer conduit 104 connecting themixing conduit loop 102 to the circulation tank 72, so that a mixedbicarbonate solution can be transferred from the mixing conduit loop 102to the circulation tank 72.

The system 100 further includes the circulation pump 76 and thecirculation supply conduit 78 which leads from the circulation tank 72to the circulation pump 76 and on to the plurality of dialysis machines106.

The system 100 further includes the circulation return conduit 80 forreturning unused mixed bicarbonate solution from the dialysis machines106 to the circulation tank 72.

The circulation supply conduit 78 and the return conduit 80 define acirculation loop 108 which also includes the various items of equipmentdisposed within the circulation loop 108.

A first heat exchanger 110 is disposed in the mixing conduit loop 102 sothat mixing conduit loop 102, the mix tank 12, the eductor 32 and themix pump 24 can be heat disinfected by circulating heated water throughthe mixing conduit loop 102.

The system 100 further includes a bypass line 112 disposed in the mixingconduit loop 102 and bypassing the first heat exchanger 110. A bypassvalve 114 is disposed in the bypass line 112.

A second heat exchanger 116 is disposed in the circulation loop 108 sothat the circulation loop 108, the circulation tank 72 and thecirculation pump 76 can be heat disinfected by circulating heated waterthrough the circulation loop 108.

The system 100 includes the wash down nozzle 66 disposed in the hopper42. A wash down line 64 connects the mixing conduit loop 102 to the washdown nozzle 66.

As previously noted, a pair of laterally offset oppositely directednozzles 54 and 56 are located inside the mix tank 12 and are connectedto the mixing conduit loop 102 to create a swirling flow of water andbicarbonate material within the mix tank 12 to mix the water andbicarbonate material thoroughly. The pair of nozzles 54 and 56, and thepiping connecting the same to the mixing conduit loop 102 areschematically shown in FIG. 5. It will be understood that the nozzles 54and 56 preferably line a generally horizontal plane and are pointed 180°apart so as to create a swirling flow in plan view when looking downinto the tank 12.

There is also a wash down nozzle 88 in the mix tank 12, and a wash downline 118 connecting the mixing conduit loop 102 to the wash down nozzle88.

A three-way control valve 120 is disposed in the mixing conduit loop 102and connects the mixing conduit loop 102 to the transfer conduit 104.The control valve 120 may be selectively moved between a first positionwherein flow goes through the mixing conduit loop 102, and a secondposition wherein flow goes from the mix pump 24 and mixing loop 102through the transfer line 104 to the circulation tank 72 in order totransfer a batch of bicarbonate solution from the mix tank 12 to thecirculation tank 72.

The mixing tank 12 preferably has a closed top 122 to preventcontamination of the fluid mixture contained therein.

The top opening 44 of the hopper 42 is preferably located no greaterthan about twenty-four to forty-eight inches above the floor from whichthe hopper 42 is supported. This allows a person operating the system100 to easily fill the hopper 42 without back strain or the like.

Each of the first and second heat exchangers are connected to a hotwater supply, such as a boiler by supply and return lines 124 and 126.The heat exchangers 110 and 116 may be described as permanently locatedwithin the circulation loop of the system 100, as contrasted to thesystem 10 of FIGS. 1, 2 and 3 wherein the analogous hot water heatersare not permanently installed, but rather are located adjacent thesystem and must be temporarily connected through the use of flexibleconduits and quick connect couplings.

It will be understood that the first and second heat exchangers 110 and116 are not in operation during the normal operation of the system 100when bicarbonate solution is being mixed and provided to the dialysismachines 106.

It is desirable, however, to periodically heat disinfect the system 100.The mixing conduit loop 102 and the various components disposed thereincan be heat disinfected separate from the circulation conduit loop 108.The first heat exchanger 110 is utilized to heat disinfect the mixingconduit loop 102, and the second heat exchanger 116 is utilized to heatdisinfect the circulation conduit loop 108.

When it is desired to disinfect the mixing conduit loop 102, thebicarbonate solution is drained from the mix tank 12 and the eductor 32and the various other components connected to the mixing conduit loop102. Then the mix tank 12 is at least partially filled with cleanpermeate. The permeate is heated by circulating the same through thefirst heat exchanger 110 while simultaneously circulating hot steam orhot water through the dirty side of heat exchanger 110 by means of hotwater supply and return conduits 124 and 126. The permeate is heated toa temperature of at least 190° F. and is then circulated through themixing conduit loop 102 for at least 15 minutes and preferably aboutone-half hour, thereby disinfecting the mixing tank 12, the eductor 32,the mixing conduit loop 102, and the various other components containedtherein.

Similarly, when it is desired to heat disinfect the circulating loop 108and the various components contained therein, the bicarbonate solutionis drained therefrom and then the circulation loop including thecirculation tank 72 is filled with clean permeate. That permeate isheated by means of the second heat exchanger 116, which receives heatfrom steam or hot water passing through the hot water supply in returnlines 124 and 126. Then the heated permeate is circulated through thecirculation loop 108 at a temperature of at least 190° F. for a time ofat least 15 minutes and preferably about one-half hour.

All of the tanks, conduits and the like of system 100 are preferablyconstructed of cross-lined polyethylene and/or polypropylene plasticmaterial. Further details of preferred heat disinfection methods aredisclosed in our co-pending application Ser. No. 09/458,140 filed onDec. 9, 1999 entitled “Heat Disinfection of a Water Supply”, the detailsof which are incorporated herein by reference.

It will be appreciated that in its broadest embodiment, the system 100discloses a method of providing bicarbonate solution from a centralizedsource 72 to a plurality of dialysis machines 106. That method includesproviding the closed mixing conduit loop 102 and the additive container42 connected to the mixing conduit loop 102. The container 42 has theopen top or loading opening 44 which can be selectively closed bycloseable cover 46.

A pre-determined quantity of the dry bicarbonate material is placedthrough the loading opening 44 into the additive container 42 and thetop 46 is then closed.

A pre-determined volume of liquid, such as clean permeate, is circulatedin the mixing conduit loop 102. As the pre-determined volume of liquidis circulated, the dry bicarbonate material is transferred from theclosed additive container 42 into the circulating liquid in the closedmixing conduit loop 102, thus dissolving the dry bicarbonate material inthe circulating permeate.

Circulation is continued and the dry bicarbonate material iscontinuously drawn into the circulating liquid until the entirepre-determined quantity of dry bicarbonate material is transferred fromcontainer 42 into the circulating conduit loop 102 and is dissolved inthe pre-determined volume of permeate liquid, thereby producing a batchof bicarbonate solution according to a pre-determined formula.

Then the batch of solution is transferred to the central supply tank orcirculation tank 72 from which it may be provided through circulationloop 108 to the plurality of dialysis machines 106.

Although in this specific embodiment disclosed herein, the dry additivecontainer 42 is a hopper associated with an eductor 32, it will beappreciated that in the broader sense of the invention other types ofclosed dry additive supplies could be utilized with the closed mixingconduit loop 102. For example, dry additive material could be providedvia a hopper and auger conveyor into a mixing tank in place of theeductor 32.

Thus, it is seen that the apparatus and methods of the present inventionreadily achieve and ends and advantages mentioned as well as thoseinherent therein. While certain preferred embodiments of the inventionhave been illustrated and described for purposes of the presentdisclosure, numerous changes in the arrangement and construction ofparts and steps may be made by those skilled in the art, which changesare encompassed within the scope and spirit of the present invention asdefined by the appended claims.

What is claimed is:
 1. A method of providing bicarbonate solution from acentralized source to a plurality of dialysis machines, comprising: (a)providing an eductor having a hopper; (b) flowing a stream of liquidthrough the eductor; (c) placing dry bicarbonate material in the hopper;(d) drawing the dry bicarbonate material into the stream of liquidflowing through the eductor to form a bicarbonate solution; (e)circulating the bicarbonate solution until the bicarbonate material isdissolved; and (f) providing the bicarbonate solution to the pluralityof dialysis machines.
 2. The method of claim 1, further comprising:providing a mixing tank and a circulation tank; said step (e) furtherincluding circulating the bicarbonate solution through the mixing tank;and said step (f) further including transferring the bicarbonatesolution to the circulation tank, and circulating the bicarbonatesolution through a circulation loop from the circulating tank to theplurality of dialysis machines and back to the circulating tank.
 3. Themethod of claim 2, further comprising: draining bicarbonate solutionfrom the circulation loop; filling the circulation loop with cleanpermeate; heating the permeate; and circulating the heated permeate inthe circulation loop and thereby disinfecting the circulation loop. 4.The method of claim 3, further comprising: said step of circulating theheated permeate including circulating the heated permeate at atemperature of at least 190° F. for at least 15 minutes.
 5. The methodof claim 3, further comprising: providing a heat exchanger permanentlylocated in the circulation loop; and said heating step including heatingthe permeate with the heat exchanger.
 6. The method of claim 2, furthercomprising: draining bicarbonate solution from the mixing tank and theeductor; filling the mixing tank at least partially with permeate;heating the permeate; circulating the heated permeate through the mixingtank and the eductor and thereby disinfecting the mixing tank and theeductor.
 7. The method of claim 6, further comprising: providing a heatexchanger; and said heating step including circulating the permeatethrough the heat exchanger.
 8. A method of providing bicarbonatesolution from a centralized source to a plurality of dialysis machines,comprising: (a) providing a closed mixing conduit loop and an additivecontainer connected to the mixing conduit loop, the container having anloading opening and a closeable cover over the opening; (b) placing apredetermined quantity of dry bicarbonate material through the loadingopening into the additive container, and closing the cover of thecontainer; (c) circulating a predetermined volume of liquid in theclosed mixing conduit loop; (d) during step (c), transferring the drybicarbonate material from the closed additive container into thecirculating liquid in the closing mixing conduit loop and dissolving thedry bicarbonate material in the circulating liquid; (e) continuing steps(c) and (d) until the entire predetermined quantity of dry bicarbonatematerial is dissolved in the predetermined volume of liquid therebyproducing a batch of bicarbonate solution according to a predeterminedformula; (f) transferring the batch to a central supply tank; and (g)providing the bicarbonate solution from the central supply tank to theplurality of dialysis machines.
 9. The method of claim 8, wherein: step(a) includes providing an eductor in the mixing conduit loop, and theadditive container is connected to the eductor; and step (d) includesdrawing the dry bicarbonate material from the additive container intothe eductor by means of a suction created by liquid flowing through theeductor.
 10. The method of claim 8, wherein: step (a) includes locatingthe loading opening of the additive container in the range of 24 to 48inches above a ground floor from which the additive container issupported.